This invention relates to a method of pressure casting, into a mold cavity, a melt quantity metered out in accordance with the volume of the cavity, by diminishing a space, receiving the metered quantity and extending between a casting gate, leading into the mold cavity, and a filling inlet in a two-phase manner including a shot pre-filling phase followed by a moldfilling phase, and to a horizontal cold-chamber die casting machine for performing the method, in which the space receiving the metered quantity of melt is constituted by a shot sleeve and the volume of the shot sleeve is diminished by an injection piston which effects the pre-filling of the shot sleeve and the discharge of the melt into the mold cavity.
At the present time, it is well known, particularly in pressure die casting, to perform the casting process using various steps of motion of the injection piston. Thus, in the course of development, in particular in cold-chamber pressure die casting, two, three, and four-phase systems have come to be known. In particular, the four phase system represents one of the newest which have appeared on the market.
The four casting phases of pressure die casting comprise, subsequently to filling of a metered quantity of the melt to be cast at a filling degree between 40 and 80% into the shot sleeve forming the receiving space in which, for example, an injection piston is moved and from which a casting gate leads into the mold cavity (1) moving the injection piston at a very low speed until the filling inlet of the shot sleeve is closed by the piston, (2) then moving the injection piston at a slightly increased, but still low, speed in order to fill the shot sleeve between the injection piston and the casting gate completely with melt, then (3) moving the injection piston at a high speed to fill the mold cavity with melt in a short time, and (4) a fourth phase including a substantially static afterpressure which is exerted on the melt filling out the mold cavity during solidification to compensate solidification shrinkage.
The very low speed during the first phase is important, particularly at high degrees of filling of the shot sleeve forming the space, to avoid spattering of the melt through the filling inlet. In the second phase, the known drawback is that, very frequently, the gas present in the shot sleeve mixes with the melt filled therein, and these gases affect the quality of the casting to be made from the melt. In the third phase, it is known to use different speeds depending on the nature of the melt and the cast piece, and also various technological criteria are taken into account, such as spraying of the casting jet, the cooling velocity of the melt, the danger of cold shots, etc. Recently, it has been found that this modern casting method does not always lead to the desired success either, particularly if castings of very high quality are to be manufactured.